The present invention relates to power transistors, and, more particularly, to microwave power transistors in which impedance matching is provided with use of a DC blocking capacitor so that transistor operation is facilitated and improved at higher microwave frequencies in the L and S bands.
Microwave power transistors are used to amplify radio frequency signals in radar and other electronic apparatus. In pulsed radar systems, numerous power transistors amplify signals for radiation, with as many as a thousand or more transistors used for this purpose and generating up to 200,000 watts or more.
Conventional microwave power transistor assemblies are hybrid structures made from a transistor die which usually includes multiple amplification elements, one or more MOS capacitor dies, and interconnections formed by bond wires which serve as assembly connection elements and as inductive elements for impedance matching between the transistor die and an output terminal of the assembly. The provision of multiple power transistors on a single transistor die provide better control of manufacturing tolerances.
As microwave power transistors are designed for operation at higher microwave frequencies, the transistor die becomes more fragile since the die must be made increasingly narrower to enable use of shorter bond wires having lower inductance values needed for impedance matching at the higher frequencies.
In the prior art, an MOS capacitor must be disposed next to the long and narrow transistor die to provide a DC block for the output parallel resonance matching circuitry. As a result, a tight positioning tolerance makes it difficult to provide an assembly which has the impedance matching and the minimum capacitor plate size needed for effective performance. Thus, the operational reliability and/or the repeatability of manufacture of higher frequency, microwave power transistors are adversely affected by known configurations of such transistors of the prior art. A conventional impedance matching configuration employs a transistor with a series inductance path connected from the transistor collector to a plate of a capacitor back-mounted on a conducting plate and with the transistor base connected to the capacitor plate.
An article entitled SILICON BIPOLAR MICROWAVE POWER TRANSISTORS, authored by Richard Allison, and published in IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOLUME MTT-27 in May 1979, provides further explanation of the conventional impedance matching configuration without disclosure of any practical structure or method for combining impedance matching circuitry integratively with an active power amplifier in a silicon chip.
Accordingly, the state of the pertaining art is such that a need exists for a better microwave power transistor structure having integrated impedance matching circuitry to operate with reproducible electrical characteristics at higher microwave frequencies.